Polishing Milled Parts

[jtrout13]

I wondered if anyone had any tips on polishing milled parts (brass and aluminum)? I can get mirror finishes easily on turned parts using my buffing wheel, but milled parts are a different story. I normally start with about 240 grit to remove tool marks, and then wet sand my way up to 800 grit and get a nice flat face on the part.

However, that's where the success ends. The buffer just doesn't seem to want to polish the part, and it ends up looking terrible (shiny in spots but with scratches that weren't there to begin with). Any ideas?

-John

 

[Tin Falcon]

I have polished lots of plastics like you said wet sand through the grits.Then I use an automotive buffing compound then a good quality plastic polish . for brass I think if you did brasso by hand and then never dull you would get what you want.
I have heard that the orange hand cleaner does wonders on aluminum maybe some of the pumice grade as a first step and smooth for the final.
As far as the buffing wheel sounds like it is dirty and has metal chips in it also may be the wrong grade of polishing compound.
Tin

 

[n4zou]

You just discovered why engine turned finishing is so popular.

 

[joe d]

John

I had the same issue, finally got a better finish on ali by doing the final buffing
with a small felt bob in the dremel with some polishing compound. For brass,
I do the final buffing with the dremel and some brasso, comes out great.

Hope this helps, and of course, YOUR mileage may vary :big:

Cheers, Joe

 

[Catminer]

John;

Don't stop at 800 grit, I wet sand 600, 1200, and finish with 2000 grit.
After that a little time with a suitable metal polish and buff with a soft rag.
Should bring a bright shine.

Peter

 

[Herbiev]

John

I also go up to 2000 grit using kerosine as the whetting agent. Then buff with Meguires or Perfect-it. They are very expensive but u get what u pay for.
Good luck

P. S. Make sure u wash the part down thoroughly between grits so as not to leave grains from previous grit causing scratches. Cleanliness is very important for a good finish

 

[milotrain]

I use a tumbler. Takes much longer but I'm sleeping while it's working. :big:

You can make one with a bucket, lid, small motor and some casters.

 

[jtrout13]

n4zou, that's some great looking engine turning you've got there.

I will have to practice on some scrap with the higher grit sandpapers and rake my buffing wheel well. I don't want to be spending much time on the actual buffing process, as I've found that too much time on the wheel leads to a 'melted butter' look on the part (features are distorted).

 

[Troutsqueezer]

I use three buffing wheels, each with a different grade of polishing compound. As for time spent on buffing process, hard to get around it. It can take as much (or more) time as it did to make the part.

 

[n4zou]

n4zou, that's some great looking engine turning you've got there.

That's not my work but I can make mine look exactly like it. All I do is cut sandpaper disks and glue them to the end of 1/2" X 3" aluminium rod and put it in the mill spindle. Then start jobbing it into the work in even increments. It's sort of like knurling on a lathe where you press knurling wheels into the surface to obtain a patterned imprint in the material. Using differing grades of sandpaper gives differing results just like fine or course knurling wheels. I cut my sandpaper plugs with 1/2" EMT conduit. It's cheap so it's disposable. I usually cut a length of conduit about 5" long and sharpen one end by hand on the grinder. The sandpaper damages the metal with every cut so you never want to use hole plug cutters such as these.

 

[jdsackett]

First, make sure all of your 240 grit scratches, or whatever the previous grit was, are gone. Very easy to miss some 240 when cutting with 600 but it will really show up when polished. I usually start with 220, go to 600, then 1500. If it's brass, i stop at 600, brass is easy to polish. Then take it to the polisher and smear some tripoly or something equivalent on a stitched wheel. Then some final rouge on a loose wheel. Works well for me. You need to understand that there is no such thing as a permanent or scratch free polish. My uncle used to make jewelry and even that had some scratches in it if you looked close enough. I have wiped a part clean with what i thought was a soft rag when i was done polishing, only to put more scratches in the finish. Oh well, if i was smart, i'd be rich. Good luck, polishing can be frustrating.

 

[Tin Falcon]

I guess everyone has there preferred grit sequence. I learned to sand and polish while doing pastern development for a boat yard . we made large patterns that the molds were made off of. so modeling in full scale. IIRC we used 80 grit to get the shape then prime sand with 180 to fair things in paint again then do 320 400 600. sometimes 1200 in some areas the molds were polished with rouge.
I generaly do the 320 400 600 sequence then a couple grades of polish.
Tin